Does the ShoreTel Server Stream Media at G711?

June 23rd, 2009

You have dutifully enable Differential Service Control Points on you WAN network, to enable EF for voice traffic!  This is the minimum daily adult requirement for QOS on a WAN connection.   Prior to Version 9+ ShoreTel did not mark all traffic with a DSCP value, only media traffic between end points.   If you think this through, what happens to the media stream played out by the ShoreTel server during Automated Attendant of Voice Mail use?  Would this media stream across the WAN using the inter-site codec setting, typically a G.729 vocoder?  Or would it stream at G.711?   Given that there is no DSCP value on this media stream, that might be a QOS problem across a WAN connection.   Would it be possible to set up a  MATC H for the source IP address of the ShoreTel Server and through these IP packets into the EF queue?

To improve this situation, ShoreTel enabled “media proxy” on the Fuji or full size 19” switches that have been shipping prior to Version 7.    In this configuration, if a caller across the WAN reached an extension at another site, and that extension RNA forwarded to the VM system, the media stream would be have different end points.  At first you would think that the media stream would be between the originating extension and the Voice Mail server, but it is not.  It is in fact, between the originating extension and a switch at the HQ site (one of the reasons you always need a switch at the HQ site).  A switch at the HQ site would then proxy the media stream to the VM server, transcoding G.711 and G.729 to assure the correct vocoder across the WAN.   In this way the, the source IP address of the server is irrelavent for QOS purposes!

Now with the introduction of the ½ size switches, this is no longer the case.  Apparently with the release of 7+ the server is capable of streaming G.729.   So we need to be aware that an installation using the new switches, will no longer proxy for the VM media stream.    Additionally, there is a requirement that you set the number of media streams that can be transcoded at any one time.   This setting is in the registry of the ShoreTel Server and should look something like this:

Path: HKEY_LOCAL_MACHINE\SOFTWARE\Shoreline Teleworks\TDIMedia

Key: MaxNoOfG729Channels

Type: DWORD

Default Value: 40

This setting is suppose to be enabled on versions 7+, but if you are upgrading you may have to create and set it manually.    Clearly, optimizing your WAN for QOS is an essential element of providing toll quality voice on any VoIP solution.   Knowing what is class marked with DSCP and what is not, is an important element of achieving the desired result.   Check this issue carefully!

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